Originally Posted by KARFA

Domestic & DUB Departure Gates
UK domestic departures and DUB departures require use of biometric facial recognition equipment and this is only fitted to certain gates at T5. For both types of flights before you enter the airside departures area your photo is taken - this happens at the gates to enter the south or north security lanes, or if you are connecting and using the FCC just before you head up to north security. When your boarding pass is scanned at the gate your photo is matched to you to ensure that the person boarding the domestic or DUB flight is the same person as went through security.

The only gates fitted with the facial recognition equipment are A1-A9, A11, A19, A22, and A23. Therefore, if you are departing on a domestic flight or DUB flight you will leave from one of these gates in T5A, or A4 if you are being bussed to a remote stand.